Ion source

ABSTRACT

An ion source includes an ion source chamber having a longitudinal axis, the ion source chamber operative to define a plasma therein. The ion source also includes a split solenoid assembly comprising a first solenoid and a second solenoid that are mutually disposed along opposite sides of the ion source chamber, where each of the first solenoid and second solenoid comprises a metal member having a long axis parallel to the longitudinal axis of the ion source chamber, and a main coil having a coil axis parallel to the long axis and comprising a plurality of windings that circumscribe the metal member. The main coil defines a coil footprint that is larger than an ion source chamber footprint of the ion source chamber.

FIELD

This disclosure relates to ion implantation and semiconductorfabrication. More particularly, the present disclosure and in particularto improved ion sources.

BACKGROUND

In high volume manufacturing processes such as semiconductor devicefabrication and solar cell manufacturing, there is a continuing need toimprove substrate throughput. This places a demand to improve throughputfor processes including ion implantation. In one example, as the size ofsilicon wafers continues to scale upwardly, ion sources having a muchlarger current output are needed to meet required wafer throughput.

Beamline ion implantation apparatus may employ indirectly heated cathode(IHC) ion sources or other sources in which an elongated aperture isused to extract an ion beam. One manner of achieving higher ion currentfor implantation is to employ an ion source having a longer extractionaperture for a given ion density so that a greater total current may beextracted from the ion source. Dipole magnets are used to generatemagnetic fields to enhance plasma density in conventional ion sourcessuch as IHC sources that have more compact extraction optics where theextraction aperture is typically less than about 100 mm in length.However, such dipole magnets do not generate desired beam uniformity inelongated ion sources where the extraction aperture is longer. In viewof the above, it will be appreciated that there is a need to improve ionimplantation apparatus, and in particular to develop ion sourcetechnology to increase the current generating capability in the ionsource while maintaining acceptable ion beam properties.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended asan aid in determining the scope of the claimed subject matter.

In one embodiment, an ion source may include an ion source chamberhaving a longitudinal axis, the ion source chamber operative to define aplasma therein. The ion source may also include a split solenoidassembly comprising a first solenoid and a second solenoid that aremutually disposed along opposite sides of the ion source chamber, whereeach of the first solenoid and second solenoid comprises a metal memberhaving a long axis parallel to the longitudinal axis of the ion sourcechamber, and a main coil having a coil axis parallel to the long axisand comprising a plurality of windings that circumscribe the metalmember. The main coil defines a coil footprint that is larger than anion source chamber footprint of the ion source chamber.

In a further embodiment, an ion implantation system for implanting asubstrate includes an ion source chamber having a longitudinal axis, theion source chamber operative to define a plasma therein. The ionimplantation system also includes a split solenoid assembly comprising afirst solenoid and a second solenoid that are mutually disposed alongopposite sides of the ion source chamber. Each of the first solenoid andsecond solenoid may include a metal member having a long axis parallelto the longitudinal axis of the ion source chamber, a main coil having acoil axis parallel to the long axis and comprising a plurality ofwindings that circumscribe the metal member, the main coil defining afootprint that covers the ion source chamber; and beam components todirect a beam of ions extracted from the ion source chamber to thesubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an ion implantation system consistent with variousembodiments of the disclosure;

FIG. 2A depicts a side view of an ion source consistent with the presentembodiments;

FIG. 2B depicts a top view of the ion source of FIG. 3A;

FIG. 2C depicts an end view of the ion source of FIG. 3A;

FIG. 3 depicts a perspective view of another ion source consistent withadditional embodiments;

FIG. 4A depicts a side view during operation of the ion source of FIG. 3consistent with the various embodiments;

FIG. 4B depicts a top view of the scenario of operation of the ionsource shown in FIG. 4A;

FIG. 4C depicts an end view of the scenario of operation of the ionsource shown in FIG. 4A;

FIG. 5A illustrates variation of magnetic field intensity in an ionsource configured according to embodiments of the disclosure;

FIG. 5B illustrates a comparison of experimental and simulated variationof magnetic field intensity in an ion source configured according toembodiments of the disclosure;

FIG. 6A depicts magnetic field in an ion source in one exemplaryconfiguration of ion source chamber and split solenoid assembly;

FIG. 6B depicts magnetic field in an ion source in another exemplaryconfiguration of ion source chamber and split solenoid assembly; and

FIG. 7 depicts an end view of another embodiment of an ion source.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention, however, may be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like numbers refer to like elements throughout.

Various embodiments involve apparatus and systems to produce highcurrent ion sources. Referring to the drawings, FIG. 1 is a blockdiagram of an ion implantation system 100 including an ion source 102. Apower supply 101 supplies the required energy to source 102 which isconfigured to generate ions of a particular species. The generated ionsare extracted from the source through a series of electrodes 104(extraction electrodes) and formed into a beam 95 which is directed andmanipulated by various beam components 95, 106, 108, 110, 112 to asubstrate. In particular, after extraction, the beam 95 passes through amass analyzer magnet 106. The mass analyzer is configured with aparticular magnetic field such that only the ions with a desiredmass-to-charge ratio are able to travel through the analyzer. Ions ofthe desired species pass through deceleration stage 108 to correctormagnet 110. Corrector magnet 110 is energized to deflect ion beamlets inaccordance with the strength and direction of the applied magnetic fieldto provide a ribbon beam targeted toward a work piece or substratepositioned on support (e.g. platen) 114. In some cases, a seconddeceleration stage 112 may be disposed between corrector magnet 110 andsupport 114. The ions lose energy when they collide with electrons andnuclei in the substrate and come to rest at a desired depth within thesubstrate based on the acceleration energy.

The present embodiments may be implemented in ion implantation systems,such as ion implantation system 100. In particular, the presentembodiments may be implemented using a novel “split solenoid” ion sourceas described herein below. FIGS. 2 to 4C depict embodiments of splitsolenoid ion sources which may be used as the ion source 102 of the ionimplantation system 100 in various embodiments. In other embodiments,the split solenoid ion sources as stand-alone devices or may be deployedin any other apparatus that employs ion sources.

The terms “split solenoid” and “split solenoid assembly” refer to aconfiguration or magnetic assembly that includes two or more separatemain coils having axes that are generally aligned parallel to oneanother, where each coil is wound round a metal piece or member. The twoor more main coils impart solenoid like properties to a region or spacebetween the two or more main coils, which space contains an ion sourcechamber. However, rather than circumferentially enclosing the ion sourcechamber as in an ideal cylindrical solenoid, the two or more “splitsolenoids” of a split solenoid assembly only bound the ion source alongseparate portions that are separated by open spaces. This facilitatesconvenient extraction of an ion beam from the ion source chamber that isbounded by the split solenoid assembly.

In a given solenoid of a split solenoid assembly, each main coilsurrounds a metal member that is relatively long in two dimensions andrelatively short in a third dimension. Notably, a main coil, togetherwith its metal member may be referred to herein as a “solenoid.” Thesolenoids may generally have a planar shape but may also be curved atleast along one direction as shown in FIG. 7. As detailed below, thismagnetic assembly is used to generate uniform magnetic fields in a spacebetween the main coils. This allows the length of such split solenoidion sources to be scaled up to a large size not achieved by conventionalby conventional dipole magnetic structures that are used to generatemagnetic fields in conventional ion sources.

Turning to FIG. 2A there is shown a side view of a split solenoid ionsource 200. FIG. 2B shows a top view of the split solenoid ion source200, while FIG. 2C shows an end view of the split solenoid ion source200. As shown in the figures, the split solenoid ion source 200 includesan ion source chamber 202, which is bounded by a split solenoid assembly203 that includes a solenoid 204 located on one side of the ion sourcechamber 202 and another solenoid 204 located on an opposite side. Theion source chamber 202 may be generally constructed according to knowntechnology. The ion source chamber 202 and solenoids may be affixed toother structures (not shown). In various embodiments the ion sourcechamber 202 may be constructed as Bernas type ion source, indirectlyheated cathode (IHC) ion source, or other type of in source. Theembodiments are not limited in this context. The ion source chamber 202is characterized by a longitudinal axis 212 (also termed “long axis”),which is parallel to the X-direction in the Cartesian coordinate systemused in the figures. The ion source chamber is generally elongated alongthis longitudinal axis 212, and may extend up to one half meter or morein some embodiments.

As illustrated, the solenoids 204 each have flat faces 214 that face oneanother and extend so as to create a footprint 216 that encompasses theion source chamber 202, as illustrated in FIG. 2B. In particular, thefootprint 216 represents a projected area of the main coils 205 in theX-Z plane. As detailed below, the solenoids 204 are configured togenerate uniform magnetic fields in the ion source chamber 202, whichfacilitates the production of more uniform ion beams, in addition toaffording scalability of such ion sources to larger dimension. In thismanner higher current ion beams having acceptable beam uniformity areachievable using the split solenoid ion source 200.

In the present embodiments, a solenoid may include a main coil and a setof optional trim coils. This is illustrated in particular in FIGS. 2A to2C, which depict a main coil 205 that is wound around a flat metal plate208. The flat metal plate 208 is elongated in a direction parallel tothe longitudinal axis 212 of the ion source chamber 202. The coil axis207 of the main coil 205 is generally parallel to the longitudinal axis212 of the ion source. The flat metal plate acts to block magneticfields generated by outer portions of each coil from extending into theregion containing the ion source chamber 202. In various embodiments theflat metal plate 208 may be a steel or similar metal. As illustrated,the flat metal plate extends beyond outer ends of the coils of eachsolenoid 204 so as to screen out magnetic fields generated by outerportion 218 of each solenoid from penetrating into the region 220between the respective solenoids 204. Accordingly, when current is sentfrom the current source 224 to the main coils 205, a magnetic field thatis generated by opposing main coils 205 and penetrates the ion sourcechamber 202 is generated from inner portions 222 of each main coil 205,as shown in FIG. 2A.

In various embodiments, in addition to the main coil 205, a pair of trimcoils 206 are included at opposite ends of each solenoid 204. As shownin FIG. 2A, the trim coil axis 209 of a trim coil 206 is aligned withthe coil axis 207 of a main coil 205. Each trim coil 206 is coupled to acurrent source 226 that is separate from the current source 224. In thismanner, the trim coils 206 are configured to receive, if desired, adifferent amount of current as compared to that sent to the main coils205. Although the current direction of current sent to the main coils205 and trim coils 206 may generally be the same, the current in trimcoils 206 may be generated in a direction opposite to that of thecurrent in main coils 205. As detailed below, the trim coils 206 may beused to adjust magnetic fields produced in the vicinity of the ionsource chamber 202.

Notably, the split solenoid ion source 200 provides advantages overconventional ion sources that employ dipole source magnets. The splitsolenoid ion source 200 in particular embodies useful properties of anideal solenoid. In an infinitely long ideal solenoid the magnetic fieldinside is homogeneous and magnetic field strength does not depend ondistance from the solenoid axis. Thus, an ideal cylindrical solenoidmagnet that encompasses an ion source chamber may produce uniformmagnetic fields therein. However, extraction of ions from an ion sourcechamber within an ideal solenoid is not practical because of thecomplete envelopment by the solenoid of the ion source chamber exceptalong its ends.

By providing a split solenoid assembly that contains two solenoids thesplit solenoid ion source 200 combines the benefits of a relativelyuniform magnetic field as in an ideal solenoid with an easily accessiblyion source chamber 202 from which a uniform ion beam may be readilyextracted, as discussed further below. In particular variants of thesplit solenoid ion source 200 may provide an almost uniform magneticfield within the ion source chamber 202, including a nearly parallelarrangement of magnetic field lines in the region of the ion sourcechamber 202 from which an ion beam is extracted. This enables theability to scale the ion source chamber 202 size by simply extending thelength of the split solenoid assembly that flanks such an ion sourcechamber.

Consistent with the present embodiments, a length of the split solenoidassembly along the longitudinal axis 212 may range from 250 mm to 2000mm, and the length L_(S) of the ion source chamber is about 100 mm to500 mm, while the aperture length L_(A) of an aperture 211 of the ionsource chamber 202 is less than or equal to L_(S). Moreover, for a givensplit solenoid ion source, such as split solenoid ion source 202, thelength of the split solenoid assembly 203 along the longitudinal axis212 is generally greater than L_(S).

Consistent with further embodiments, FIG. 3 depicts a perspective viewof another split solenoid ion source 250 in operation. The splitsolenoid ion source 250 contains an ion source chamber 252 and a splitsolenoid assembly 253 that includes a pair of solenoids 255 that extendon two opposite sides of the ion source chamber 252. In this embodiment,the solenoids 255 each include a main coil 256 and a pair of trim coils258 that are arranged similarly to the arrangement of a split solenoidshown in FIGS. 2A-2C. In particular the main coils 256 and trim coils258 are each wound around an elongated flat metal member 260 whose longdirection extends parallel to the longitudinal axis 262 of the ionsource chamber 252. When current is drawn through the solenoids 255 auniform magnetic field 272 is generated through the center of the ionsource chamber 252. As further illustrated in FIG. 3, when a plasma (notshown) is generated in the ion source chamber 252 an ion beam containingthe ions 264 may be extracted from the ion source chamber. Due to theuniform magnetic field 272, the ion beam may be uniform over its widthwhen extracted.

FIGS. 4A, 4B, and 4C depict a side view, top view, and end viewrespectively of the split solenoid ion source 250 that highlight furtheradvantages of the present embodiments. In FIG. 4A, an aperture 254 inthe ion source chamber 252 is also depicted. Referring also to FIG. 4C,ions generated in a plasma 266 are extracted through the aperture 254and may be accelerated by an extraction system (not shown) to direct theions 264 as a beam of ions having a desired energy. The aperture 254 ischaracterized by an aperture length L_(A) along the longitudinal axis262 of the ion source chamber 252. The length of the aperture may beused to define the initial size or width of the ion beam formed by ions264 as the ions 264 are extracted from the ion source chamber 252.

By scaling upwardly the length L_(S) of the ion source chamber 252, theaperture length L_(A) can be concomitantly scaled upwardly to increasethe size of a beam of ions 264. For a given plasma density, this maylead to a proportional upward scaling of ion current with increasedL_(S). Because such an ion source chamber in principle only needs anincrease in length along the X-direction, scaling of ion sourcesconstructed according to the present embodiments for larger currentproduction is straightforward. In the example particularly illustratedin FIG. 4A, the length L_(S) of the ion source chamber 252 is 325 mm. Anexperimental embodiment has produced an operational ion source chamberof similar dimensions having an aperture length L_(A) of 250 mm for anIHC ion source, thereby increasing the current capability overconventional IHC ion sources that are typically less than 100 mm inlength. For example, a conventional apparatus based upon an IHC sourcehaving a 55 mm extraction aperture yields about 50 mA current, while anapparatus designed according to the present embodiments having a 225 mmaperture yields 120 mA or more of high quality beam current.

In addition, the present embodiments provide for increased uniformity ofmagnetic fields within an ion source even when sources are scaled tolarge dimensions, such as dimensions greater than 100 mm in length. FIG.5A compares magnetic uniformity of a split solenoid ion sourceconstructed according to the present embodiments with that of aconventional dipole magnet ion source. The curve 502 represents themagnetic field strength (in Tesla) as a function of position for adipole magnet source showing the calculated variation in magnetic fieldin a middle region of an ion source along the X-direction over a 350 mmrange, which approximates the length of the aforementioned 325 mm IHCsource. In this case the magnetic field strength is greatest at theextremities of the ion source (−175 mm and +175 mm) and decreases byabout two thirds at the center region.

In contrast to this extreme non-uniformity in magnetic field strength,the curves 504 and 506 present calculated magnetic field strength for asplit solenoid ion source over the same range as for the dipole magnetcase, showing that magnetic strength varies by less than 10% over theentire 350 mm range. Magnetic fields of about 200 Gauss (0.02 Tesla) areachievable in embodiments of a split solenoid ion source. In particular,the curve 504 represents magnetic field strength when no current issupplied to the trim coils while curve 506 represents magnetic fieldstrength when a fixed amount of current is supplied to the trim coils.When no current is supplied to the trim coils, the magnetic fieldstrength (curve 504) exhibits a “frown” shape in which magnetic fieldstrength peaks in the center, while when a specific amount of current issupplied to the trim coils the magnetic field strength (curve 506)exhibits a “smile” shape in which the magnetic field strength reaches aminimum in the center. It is to be noted that the level of currentsupplied to trim coils may be used to further adjust the shape ofmagnetic field strength as a function of position so that the frown ofsmile can be minimized.

FIG. 5B provides further details showing a comparison of simulated andexperimental data for magnetic field strength uniformity produced in asplit solenoid ion source. The curve 512 illustrates simulated magneticfield strength along the X-direction with no trim coil current, whilethe curve 514 illustrates measured magnetic field strength with no trimcoil current. The curve 516 illustrates simulated magnetic fieldstrength with trim coil current, while the curve 518 illustratesmeasured magnetic field strength with trim coil current. In the case ofcurve 518, when trim coil current is applied, the maximum variation inmagnetic field strength is only about 5%.

In addition to reducing variation in magnetic field strength along thelong direction (parallel to the X-axis) of an ion source, the splitsolenoid ion source design of the present embodiments facilitates theability to adjust the magnetic field direction in different portions ofan ion source for optimal beam geometry. FIGS. 6A and 6B present theresults of simulation of magnetic field shape in an ion source chamber602 for a split solenoid ion source consistent with the presentembodiments. The figures present a top view in the X-Z plane where theion beam (not shown) exits toward the top of the page. In FIG. 6A, asplit solenoid ion source 600 includes the ion source chamber 602 whosecenter along the Z-direction is aligned with the longitudinal axis 606of the split solenoid 604. When the ion source chamber 602 has itscenter aligned with the center of the split solenoid 604, the magneticfield lines 608 (shown in dashed form) near the faceplate (faceplate andextraction apparatus are not shown) edge 610 are substantially curved,showing an outward bulge toward the center of the faceplate edge 610.Because the faceplate edge 610 is disposed toward the extraction side612 where ions exit the split solenoid ion source 600, magnetic fieldline curvature may affect the trajectories of exiting ions.

In FIG. 6B, a split solenoid ion source 620 includes the same ion sourcechamber 602 whose center is now shifted forward by 15 mm along theZ-direction with respect to the longitudinal axis 606 of the splitsolenoid 604. In this case, the magnetic field lines 608 near thefaceplate edge 610 are substantially straight. This latter embodimentmay be useful where it is desired to generate parallel ion trajectoriesacross a width of an ion beam extracted from the split solenoid ionsource.

In addition to the generally planar split solenoid ion sources disclosedhereinabove, the present embodiments include solenoid ion sources inwhich a pair of solenoids have a curved cross-section as illustrated inFIG. 7. The split solenoid ion source 700 of FIG. 7 may have the generalshape of the split solenoid ion source 200 except that the opposing pairof solenoids 702 are curved as viewed along the end view shown. In thiscase, each coil 704 surrounds a curved (though not planar) plate 706.The solenoids 702 are generally curved inwardly so as to lie on portionsof a curve that surround the ion source chamber 202.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Further, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes.

What is claimed is:
 1. An ion source, comprising: an ion source chamberhaving a longitudinal axis, the ion source chamber operative to define aplasma therein; a split solenoid assembly comprising a first solenoidand a second solenoid that are mutually disposed along opposite sides ofthe ion source chamber, each of the first solenoid and second solenoidcomprising: a metal member having a long axis parallel to thelongitudinal axis of the ion source chamber, and a main coil having acoil axis parallel to the long axis and comprising a plurality ofwindings that circumscribe the metal member, the main coil defining acoil footprint that is larger than an ion source chamber footprint ofthe ion source chamber.
 2. The ion source of claim 1, further comprisinga first current source coupled to the first solenoid and second solenoidwherein the first and second solenoid are interoperative to generate amagnetic field that extends substantially parallel to the longitudinalaxis when the first current source transmits a main current to the firstand second solenoid.
 3. The ion source of claim 1, wherein the first andsecond solenoid each further comprise: a first trim coil and second trimcoil disposed at opposite ends of a respective solenoid and defining atrim coil axis concentric with the coil axis of a respective solenoid.4. The ion source of claim 3, further comprising a second current sourceseparate from the first current source and coupled to the first andsecond trim coils, wherein first and second trim coils are configured toadjust a magnetic field profile of the ion source that comprisesvariation in magnetic field intensity in the ion source chamber alongthe longitudinal axis, wherein when the second current source supplies afirst trim coil current, a resulting first magnetic profile comprises arelatively higher magnetic field intensity in a middle region of the ionsource chamber as compared to end portions of the ion source chamber,and wherein when the second current source supplies a second trim coilcurrent, a resulting second magnetic profile comprises a relativelylower magnetic field intensity in a middle region of the ion sourcechamber as compared to end portions of the ion source chamber.
 5. Theion source of claim 3, further comprising a second current sourceseparate from the first current source and coupled to the first andsecond trim coils, the second current source configured to supply a trimcoil current that travels in a first configuration, in a same directionas a main coil current of the solenoid generated by the main coils ofthe split solenoid assembly, and in a second configuration in anopposite direction as the main coil current of the solenoid.
 6. The ionsource of claim 1, wherein the split solenoid assembly comprising alength along the longitudinal axis of about one 250 mm to 2000 mm, andthe ion source chamber comprising an ion source length along thelongitudinal axis of about 100 mm to 500 mm.
 7. The ion source of claim1, further comprising an extraction assembly configured to extract anion beam from the ion source chamber having a beam width of greater thanor equal to 100 mm.
 8. The ion source of claim 1, wherein the splitsolenoid assembly operative to generate a magnetic field substantiallyparallel to the longitudinal axis of the ion source chamber along anextraction edge of the ion source from which an ion beam exits the ionsource chamber.
 9. The ion source of claim 1, wherein the ion sourcecomprising an ion extraction side from which ions exit the ion source,wherein a center of ion source chamber is displaced toward the ionextraction side with respect to a long axis of the metal member.
 10. Theion source of claim 1, wherein the ion source chamber comprising anindirectly heated cathode ion source chamber.
 11. An ion implantationsystem for implanting a substrate, comprising: an ion source chamberhaving a longitudinal axis, the ion source chamber operative to define aplasma therein; a split solenoid assembly comprising a first solenoidand a second solenoid that are mutually disposed along opposite sides ofthe ion source chamber, each of the first solenoid and second solenoidcomprising: a metal member having a long axis parallel to thelongitudinal axis of the ion source chamber, a main coil having a coilaxis parallel to the long axis and comprising a plurality of windingsthat circumscribe the metal member, the main coil defining a footprintthat covers the ion source chamber; and beam components to direct a beamof ions extracted from the ion source chamber to the substrate.
 12. Theion implantation system of claim 11, further comprising a first currentsource coupled to the first solenoid and second solenoid wherein thefirst and second solenoid are interoperative to generate a magneticfield that extends substantially parallel to the longitudinal axis whenthe first current source transmits a main current to the first andsecond solenoid.
 13. The ion implantation system of claim 11, whereinthe split solenoid assembly comprises a length along the longitudinalaxis of about 0.5 meters to two meters, and the ion source chambercomprising an ion source length along the longitudinal axis of about 0.2to 0.5 meters.
 14. The ion implantation system of claim 11, wherein theion source further comprises an extraction assembly configured toextract an ion beam from the ion source chamber having a beam width ofgreater than about 0.1 meters.
 15. The ion implantation system of claim11, wherein the ion source chamber comprises an indirectly heatedcathode ion source chamber.